Tolerability and Toxicity of High-precision Postoperative External Beam Radiation Therapy for Locally Advanced Thyroid Malignancy: A Single-center Study

A BSTRACT Introduction: Surgical resection remains the primary treatment for all thyroid cancers. Traditionally, adjuvant therapy with external beam radiation therapy (EBRT) is considered in locally advanced cases, although its role remains undefined. This study aims to evaluate the tolerance, toxicity, and outcomes of EBRT in locally advanced thyroid cancer when delivered using high-precision techniques. Materials and Methods: This retrospective study included all postoperative thyroid cancer patients treated between 2018 and 2023 who received adjuvant EBRT with high-precision techniques as recommended by a multidisciplinary tumor board for indications including residual disease, extra-thyroidal extension, recurrence, and tracheal involvement. Descriptive statistics of demographic details, Kaplan–Meier survival analysis of outcome measures, and univariate analysis of major prognostic factors were performed. Results: Our study included 52 patients, with the most common histology (75%) being papillary thyroid carcinoma. The most common indication (67.3%) for postoperative EBRT was the presence of gross residual disease. EBRT doses of 60–70 Gy in 30–35 fractions were well tolerated, and most patients (88.5%) completed treatment without significant treatment breaks. During EBRT, some patients (30.8%) experienced Grade 3 acute toxicities, with dermatitis being the most common (13.5%). Late side effects included esophageal stricture (3.8%) and tracheal stenosis (3.8%). The median follow-up was 23.5 months (interquartile range: 13–44.8), and 3 patients (5.7%) were lost to follow-up. The 2-year overall survival, distant metastasis-free survival, recurrence-free survival (RFS), and locoregional recurrence-free survival (LR-RFS) were 98%, 89.8%, 89.8%, and 95.9%, respectively. Conclusion: Our study shows that EBRT with high-precision techniques for locally advanced thyroid cancer demonstrates good tolerance, acceptable toxicity, and favorable outcomes. Careful patient selection is critical to balance disease control and treatment-related morbidity, supporting the use of EBRT in selected cases following multidisciplinary evaluation.